The present invention relates to an optical pickup for use in a disk player such as a DVD or CD, and more particularly concerns a technique which makes it possible to reliably fix a half mirror to a predetermined position on a housing by a simple arrangement.
As an example of an optical pickup, one shown in FIG. 5 is known. In this optical pickup, a half mirror 3 is disposed in an inclined state midway in a groove portion 2 formed in a housing 1, and an objective lens OL and a collimator lens QWP, on one hand, and a chip 4 with a photodiode PD, on the other hand, are respectively disposed at both ends of the housing 1 with the half mirror 3 disposed therebetween. A semiconductor laser LD is provided on a side surface of the housing 1. An arrangement is provided such that laser light is projected onto a disk D from the semiconductor laser LD through the half mirror 3, the collimator lens QWP, and the objective lens OL, and the light reflected therefrom is received by the photodiode PD, thereby reading information recorded in the disk D.
As shown in FIGS. 6 to 8, a retaining seat 6 having an inclined side surface 6a and an inclined end surface 6b, which are disposed in such a manner as to oppose each other in an L-shape, is formed on one side surface of the groove portion 2. Meanwhile, a positioning seat 7 having an inclined side surface 7a, which is flush with the inclined side surface 6a of the retaining seat 6, is formed on the other side surface of the groove portion 2.
As shown in FIGS. 6 to 8, the half mirror 3 has a rectangular block shape, a rear surface 3a of the half mirror 3 is made to abut against a bottom surface 2a of the groove portion 2, and one end portion 3b thereof is made to abut against the inclined side surface 6a and the inclined end surface 6b of the retaining seat 6, while the other end portion 3c thereof is made to abut against the inclined side surface 7a of the positioning seat 7. Thus the half mirror 3 is disposed in such a manner as to diagonally traverse the groove portion 2.
As a technique for fixing the half mirror 3, one disclosed in the Examined Japanese Utility Model Application Publication No. Hei3-4977 and the like is conventionally known. One of its examples will be described with reference to FIGS. 6 to 8. In this example, an ultraviolet curing adhesive 8 is applied to three spots between the rear surface 3a of the half mirror 3 and the bottom surface 2a of the groove portion 2 and between each of both end portions 3b and 3c of the half mirror 3 and each of the seats 6 and 7, and ultraviolet rays are applied thereto to cure the adhesive 8. The half mirror 3 is thereby fixed so as not to move unexpectedly in the left-and-right directions a and b, back-and-forth directions c and d, and vertical directions e and f.
In the above-described conventional arrangement, the half mirror 3 is bonded at three spots by the adhesive 8, and since the amount of the adhesive 8 applied to each spot is difficult to be set to a fixed amount or less, the amount of bonding becomes large. Accordingly, there is a possibility that the half mirror 3 is pulled by the shrinking force due to the curing of the adhesive 8 and becomes offset from its predetermined position.
In addition, since the half mirror 3 is placed in the inclined state, the adhesive 8 applied between the rear surface 3a of the half mirror 3 and the bottom surface 2a of the groove portion 2 is likely to flow down at a position g along an upper surface 3d of the half mirror 3. For this reason, the bonding of the rear surface 3a of the half mirror 3 and the bottom surface 2a of the groove portion 2 is likely to become insufficient. Further, the adhesive 8 which flowed down along the upper surface 3d is accumulated in a relatively large amount in a recessed portion 9 between the half mirror 3 and the groove portion 2, so that there is a possibility that the half mirror 3 is pulled by the shrinking force due to the curing of the accumulated adhesive 8 and becomes offset from its predetermined position.